1. Field of the Invention
The present disclosure relates generally to rolls used in electrophotography, and, more specifically, to a process of manufacture for a roll having a surface with uniform electrical properties around its circumference.
2. Description of the Related Art
Image forming devices, such as printers, copiers, fax machines, etc., utilize a number of components to transfer toner from a toner reservoir to a photoconductor and ultimately to a sheet of paper, or other media. For example, a photoconductor may be charged utilizing a charging device and selectively discharged to form a latent image thereon. Toner may then be transferred onto the photoconductor from the reservoir via differential charging of the photoconductor, toner and developer rolls or transfer rollers. From the photoconductor, toner may then be deposited onto a sheet of paper, creating the desired image. The transferred toner may then be fused to the paper by a fuser or other fixation device or process.
Developer rolls may be solid or two-layer and may comprise a cast urethane which may be formed of a polydiene, such as polyisoprene and more specifically polybutadiene, either as a polyol or a urethane prepolymer, blended with a second polyurethane prepolymer and a conductive additive such as ferric chloride. A resistive surface layer can be produced on a cast urethane roll by baking in air at an elevated temperature. The oxidation of polybutadiene, in the presence of certain conductive metal salts, may produce a layer at the surface of the roll having relatively highly electrical resistance. The thickness and resistivity of this layer may be adjusted by varying, for instance, the polybutadiene and metal salt concentrations in the urethane, the baking time, the baking temperature, and the concentration of oxygen.
A blend of urethane precursor materials may be cast into a mold around a conductive metal shaft to form a roll, cured at a high temperature, processed via grinding to the required functional dimensions, and then baked at an elevated temperature (e.g., >80° C.) to oxidize the surface of the roller. This controlled oxidation produces a layer on the outside surface of the roll having relatively high resistivity.
Such cast urethane rolls are disclosed in U.S. Pat. Nos. 5,707,743; 5,804,114 and 5,874,172 as well as United States Patent Application Publication No. 2007/0021583, all commonly assigned to the assignee of the present disclosure and include herein in their entirety by reference.